X-ray diffractometer

ABSTRACT

An X-ray diffractometer has an X-ray source for producing an X-ray beam; a position sensitive detector for detecting diffracted X-rays over a wide angle; and means for effecting controlled relative rotation between the detector and the X-ray source incident beam. A sample holder is capable of rotation about three mutually perpendicular axes and is also capable of providing rotation of the sample relative to the sample holder about two perpendicular axes. Thin films or substrates under investigation can be individually aligned into selected diffraction geometries by such a diffractometer. The X-ray source itself may be rotatable about the axis of the X-ray beam.

The present invention relates to X-ray diffractometers for use ininvestigation of sample such as single crystals, thin films and surfacesand the like, using position-sensitive detectors.

In GB patent application no. 8929306.2 (GB-A-2228167) the presentinventor describes an X-ray diffractometer which comprises a source ofX-rays for producing an incident beam falling on a sample to beinvestigated, a position-sensitive detector which has a wide aperture todetect the diffracted X-rays over a wide angular coverage, and means foreffecting controlled relative rotation between the detector and theincident beam to increase the effective area of detection covered by thedetector.

Various embodiments of the diffractometer are described and claimed.

Other prior art of interest comprises the following patentspecifications: GB-A-2081440, GB-A-774572; EP-A-0207863; EP-A-0115891;and EP-A-0015475. In each of these prior patent specifications, there isshown relative movement between the X-ray source, the sample underinvestigation, or the detector. In EP-A-0207863 in particular, thesample is shown to be supported on a three axis stage. Theposition-sensitive detector is generally arcuate and the X-ray source ifmovable arcuately about an axis through the sample and lying in the sameplane as the arc of the detector. Other art of possible relevanceincludes U.S. Pat. No. 3,105,901, EP-A-0165877 and Zeitschrift furMetallkunde Vol. 75, no. 2, February 1984.

The present inventor has now appreciated that significant advantages areto be gained by providing additional freedoms of movement in adiffractometer of the type described and claimed in GB-A-2228167.

In accordance with a first aspect of the present invention therefore anX-ray diffractometer comprising an X-ray source for producing an X-raybeam; a position sensitive detector for detecting diffracted X-rays overa wide angle; and means for effecting controlled relative rotationbetween the detector and the X-ray source incident beam, ischaracterised by means for mounting the X-ray source for rotation aboutthe axis of the X-ray Ream emitted therefrom.

By allowing rotation of the X-ray source so that the incident beam(which is much narrower in one dimension of the cross-section than inthe other) can be arranged to lie with its longer dimension either inthe arcuate plane of the detector (see GB PA 8929306.2) or perpendicularto it. By this means, in the latter orientation of the X-ray source, athin film sample in particular, having a planar surface disposedperpendicularly to the plane of the incident beam, can be investigatedin an optimum way.

According to a second aspect of the present invention, an X-raydiffractometer comprising an X-ray source for producing an X-ray beam; aposition sensitive detector for detecting diffracted X-rays over a wideangle; and means for effecting controlled relative rotation between thedetector and the X-ray source incident beam, is characterised by;

a sample holder capable of rotation about three mutually perpendicularaxis; and means for providing rotation of the sample relative to thesample holder about two perpendicular axes, whereby thin films orsubstrates under investigation can be individually aligned into selecteddiffraction geometries.

One example of an X-ray diffractometer according to the presentinvention will now be described with reference to the accompanyingdrawings in which:

FIGS. 1 & 2 and 3 & 4 are copies of FIGS. 1 & 2 and 5 & 6 of thedrawings from GB-A-2228167;

FIG. 5 is a diagrammatic side view illustrating the application of thesecond aspect of the present invention to the apparatus shown in GBpatent application 8929306.2; and,

FIGS. 6 to 9 illustrate how the first aspect of the present invention isapplied to that apparatus.

FIG. 1 illustrates the basic X-ray diffractometer described in GB patentapplication 8929306.2, the diffractometer comprising an X-ray source 1,a sample support 2 and an arcuate, position-sensitive X-ray detector 3.A sample, often a crystal 4, is mounted on the sample support 2 and theearlier application describes, with reference to FIGS. 2, 3 and 4 inparticular, how it is possible to rotate the sample and the detectorrelative to one another and to the X-ray source.

In the investigation of crystalline samples, thin films etc.,illumination of the sample by an X-ray beam from the X-ray source ortube 1, causes interference patterns to be generated on the surface ofthe detector, the detector thus being used to measure the scatteringorientation and intensity of the incident X-rays.

The earlier patent application describes how the sample and detector aremounted on a common base which can be rotated around a substantiallyvertical axis through the sample, to obtain signals for investigation.The common axis of rotation of the sample and detector is arranged to beperpendicular to the central axis of symmetry of the detector and thuslies in the plane of the arcuate curve of the detector. The aperture ofthe detector is adjustable for optimising the angular resolution of theinstrument and the sample can be rotated about three mutually orthogonalaxis by a multi-axis motor-controlled gimbal or goniometer.

FIG. 5 is a diagrammatic illustration of an example of thediffractometer of the earlier application referenced above, in whichrotation of the X-ray source as desired, is provided for (and alsorotation of the sample if desired), by a bearing 1', in order to providefor enhanced detection of diffracted X-rays, particularly when examiningthin films and substrates. The beam of X-rays emitted by the X-raysource tube 1 has an elongate cross-section (the beam is seen face on inFIG. 5) and thus, by rotating the X-ray tube 1, the beam can be turnedon its axis relative to the sample which is mounted on the bottom of thesample holder 5, the holder 5 being rotatable about three axes andtherefore enabling the beam to be directed at the required angle and inthe required orientation onto the sample. This is particularly importantwhen investigating thin film samples. The holder 5 can be tilted in thegimbal assembly to any desired angle as illustrated in FIG. 3 and byreference to FIG. 7.

FIG. 6 is a diagrammatic perspective view of the apparatus of theinvention and FIG. 7 is a plan view of the sample table area. Thesefigures illustrate how the three mutually orthogonal axes of rotation ofthe sample holder may be provided in accordance with the earlierapplication. (Rotation of the X-ray beam about its axis is achieved byrotation of the x-y slit through which it is emitted, but, forsimplicity is not shown in these figures.) FIG. 7 shows the generallycylindrical sample holder 5 with the sample attached in use to its lowerplanar face (see FIG. 9), the sample being rotatable about the centrallongitudinal axis Z--Z of the cylinder (known as the ζ movement) by astepper motor (motor ζ) driving the sample holder through a gear wheel5', and the two other axes X--X, Y--Y of rotation of the sample table 8being provided by gimbal bearings 6,7 and respective stepper motors(motor φ, motor θ), each of which gimbal bearings is normally containedin the plane of the sample table 8 which holds the sample holder 5.Relative rotational movement between the sample table 8, gimbal frame 9and main table 10 is provided by the stepper motors driving suitablescrew-threaded couplings 6',7' to provide fine adjustment.

In addition, the sample table 8 is movable translationally in the x andy directions by two further stepper motors (motor x, motor y).

FIGS. 8 & 9 illustrate, in side section and plan view respectively, howtwo further axes of rotation are provided for to cater for fineadjustment of the position of the sample relative to the sample table 8.The sample holder 5 is a hollow cylinder open at its top end and carriesthree adjusting screws 11 which are in screw-threaded engagement withthe base 12 of the cylinder 5. The adjusting screws 11 carry a sampleplate 13 on which is mounted the sample 14. The adjusting screws areequiangularly disposed about the centre axis of the sample holder 5, sothat adjustment of the position of the plate 13 in the two axesperpendicular to the longitudinal axis of the sample holder can beeffected. Although the screws are shown as manually operated in FIG. 9,the screws could be stepper motor driven if desired.

I claim:
 1. An X-ray diffractometer for investigating samples of thethin film and substrate type comprising:an X-ray source for producing anX-ray source incident beam; a position sensitive detector for detectingdiffracted X-rays over a wide angle; means for effecting controlledrelative rotation between the detector and the x-ray source incidentbeam to a selected position and orientation, a sample holder capable ofrotation about three mutually perpendicular axes; and means forselectively positioning the sample for irradiation in a fixed positionrelative to the sample holder about two perpendicular axes forindividually aligning the samples under investigation into selecteddiffraction geometries for the corresponding thin film and substratetypes.
 2. A diffractometer according to claim 1, comprising: steppermotor means for effecting relative rotation between the detector and theX-ray source and rotation of the sample holder about the three mutuallyperpendicular axes resulting in selective rotational and translationalmovements thereof.
 3. A diffractometer according to claim 1, wherein thesample holder (5) is rotatably supported in a sample table (8), aboutits axis and normal to the plane of the sample table, the sample tablebeing gimballed about a first axis in a gimbal frame (9) which, in turn,is gimballed in a main frame (10), about a second axis at 90° to thefirst.
 4. A diffractometer according to claim 3, further including means(x,y) for supporting the sample table for controllable translation alongtwo perpendicular axes which lie in the plane of the sample table.
 5. Adiffractometer according to claim 3, wherein the sample (14) issupported on a mount (13) in the sample holder, the mount beingadjustably positioned in the sample holder by means of adjustment screws(11) by means of which the position of the mount can be adjusted about apair of axes lying in the plane of the mount.
 6. A diffractometeraccording to comprising: stepper motor means for effecting relativerotation between the detector and the X-ray source and rotation of thesample holder about the three mutually perpendicular axes resulting inselective rotational and translational movements thereof.
 7. Adiffractometer according to claim 1, wherein the sample is supported ona mount in the sample holder, the mount being adjustably positioned inthe sample holder by means of adjustment screws by means of which theposition of the mount can be adjusted about a pair of axes lying in theplane of the mount.
 8. An X-ray diffractometer comprising an X-raysource (1) for producing an X-ray beam; a position sensitive detector(3) for detecting diffracted X-rays over a wide angle; and means foreffecting controlled relative rotation between the detector and theX-ray source incident beam, characterised bymeans (1') for mounting theX-ray source for rotation about the axis of the X-ray beam emittedtherefrom.